Adding an App in Settings>Passwords>Autofill?

I have an application that requires a login. I would like to use my iPhone 13 Pro Max’s built-in password manager in iOS 15 to save the password and recall it in order to login.

If I go to Settings>Passwords>Autofill and hit the + to add a new password entry, the only option I get is to add a username and password for a website, but NOT an app.

if I try to add the name of the app, I’m not able to hit the done button unless I add a.com, which doesn’t work.

is there a way to use the password manager to login to apps on my phone?

Thanks for any insights or suggestions.